Characterization of the extracellular domain of sensor histidine kinase NagS from Paenibacillus sp. str. FPU-7: nagS interacts with oligosaccharide binding protein NagB1 in complexes with N, N'-diacetylchitobiose.

We have previously isolated the Gram-positive chitin-degrading bacterium Paenibacillus sp. str. FPU-7. This bacterium traps chitin disaccharide (GlcNAc)2 on its cell surface using two homologous solute-binding proteins, NagB1 and NagB2. Bacteria use histidine kinase (HK) of the two-component regulatory system as an extracellular environment sensor. In this study, we found that nagS, which encodes a HK, is located next to the nagB1 gene. Biochemical experiments revealed that the NagS sensor domain (NagS30-294) interacts with the NagB1-(GlcNAc)2 complex. However, proof of NagS30-294 interacting with NagB1 without (GlcNAc)2 is currently unavailable. In contrast to NagB1, no complex formation was observed between NagS30-294 and NagB2, even in the presence of (GlcNAc)2. The NagS30-294 crystal structure at 1.8 Å resolution suggested that the canonical tandem-Per-Arnt-Sim fold recognizes the NagB1-(GlcNAc)2 complex. This study provides insight into the recognition of chitin oligosaccharides by bacteria.

A selective hybrid fluorescent sensor for fructose detection based on a phenylboronic acid and BODIPY-based hydrophobicity probe.

Fructose is widely used in the food industry. However, it may be involved in diseases by generating harmful advanced glycation end-products. We have designed and synthesized a novel fluorescent probe for fructose detection by combining a phenylboronic acid group with a BODIPY-based hydrophobicity probe. This probe showed a linear fluorescence response to d-fructose concentration in the range of 100-1000 µM, with a detection limit of 32 µM, which is advantageous for the simple and sensitive determination of fructose.

Structural characterization of two solute-binding proteins for N,N'-diacetylchitobiose/N,N',N''-triacetylchitotoriose of the gram-positive bacterium, Paenibacillus sp. str. FPU-7.

The chitinolytic bacterium Paenibacillus sp. str. FPU-7 efficiently degrades chitin into oligosaccharides such as N-acetyl-D-glucosamine (GlcNAc) and disaccharides (GlcNAc)2 through multiple secretory chitinases. Transport of these oligosaccharides by P. str. FPU-7 has not yet been clarified. In this study, we identified nagB1, predicted to encode a sugar solute-binding protein (SBP), which is a component of the ABC transport system. However, the genes next to nagB1 were predicted to encode two-component regulatory system proteins rather than transmembrane domains (TMDs). We also identified nagB2, which is highly homologous to nagB1. Adjacent to nagB2, two genes were predicted to encode TMDs. Binding experiments of the recombinant NagB1 and NagB2 to several oligosaccharides using differential scanning fluorimetry and surface plasmon resonance confirmed that both proteins are SBPs of (GlcNAc)2 and (GlcNAc)3. We determined their crystal structures complexed with and without chitin oligosaccharides at a resolution of 1.2 to 2.0 Å. The structures shared typical SBP structural folds and were classified as subcluster D-I. Large domain motions were observed in the structures, suggesting that they were induced by ligand binding via the "Venus flytrap" mechanism. These structures also revealed chitin oligosaccharide recognition mechanisms. In conclusion, our study provides insight into the recognition and transport of chitin oligosaccharides in bacteria.

Functional analysis of α-1,3-glucanase domain structure from Streptomyces thermodiastaticus HF3-3.

α-1,3-Glucanase from Streptomyces thermodiastaticus HF3-3 (Agl-ST) has been classified in the glycoside hydrolase (GH) family 87. Agl-ST is a multi-modular domain consisting of an N-terminal ß-sandwich domain (ß-SW), a catalytic domain, an uncharacterized domain (UC), and a C-terminal discoidin domain (DS). Although Agl-ST did not hydrolyze α-1,4-glycosidic bonds, its amino acid sequence is more similar to GH87 mycodextranase than to α-1,3-glucanase. It might be categorized into a new subfamily of GH87. In this study, we investigated the function of the domains. Several fusion proteins of domains with green fluorescence protein (GFP) were constructed to clarify the function of each domain. The results showed that ß-SW and DS domains played a role in binding α-1,3-glucan and enhancing the hydrolysis of α-1,3-glucan. The binding domains, ß-SW and DS, also showed binding activity toward xylan, although it was lower than that for α-1,3-glucan. The combination of ß-SW and DS domains demonstrated high binding and hydrolysis activities of Agl-ST toward α-1,3-glucan, whereas the catalytic domain showed only a catalytic function. The binding domains also achieved effective binding and hydrolysis of α-1,3-glucan in the cell wall complex of Schizophyllum commune.

Mutagenesis and structure-based analysis of the role of Tryptophan525 of γ-glutamyltranspeptidase from Pseudomonas nitroreducens.

γ-Glutamyltranspeptidase (GGT) is a ubiquitous enzyme that catalyzes the hydrolysis of the γ-glutamyl linkage of γ-glutamyl compounds and the transfer of their γ-glutamyl moiety to acceptor substrates. Pseudomonas nitroreducens GGT (PnGGT) is used for the industrial synthesis of theanine, thus it is important to determine the structural basis of hydrolysis and transfer reactions and identify the acceptor site of PnGGT to improve the efficient of theanine synthesis. Our previous structural studies of PnGGT have revealed that crucial interactions between three amino acid residues, Trp385, Phe417, and Trp525, distinguish PnGGT from other GGTs. Here we report the role of Trp525 in PnGGT based on site-directed mutagenesis and structural analyses. Seven mutant variants of Trp525 were produced (W525F, W525V, W525A, W525G, W525S, W525D, and W525K), with substitution of Trp525 by nonaromatic residues resulting in dramatically reduced hydrolysis activity. All Trp525 mutants exhibited significantly increased transfer activity toward hydroxylamine with hardly any effect on acceptor substrate preference. The crystal structure of PnGGT in complex with the glutamine antagonist, 6-diazo-5-oxo-l-norleucine, revealed that Trp525 is a key residue limiting the movement of water molecules within the PnGGT active site.

Identification of quasi-stable water molecules near the Thr73-Lys13 catalytic diad of Bacillus sp. TB-90 urate oxidase by X-ray crystallography with controlled humidity.

Urate oxidases (UOs) catalyze the cofactor-independent oxidation of uric acid, and an extensive water network in the active site has been suggested to play an essential role in the catalysis. For our present analysis of the structure and function of the water network, the crystal qualities of Bacillus sp. TB-90 urate oxidase were improved by controlled dehydration using the humid air and glue-coating method. After the dehydration, the P21212 crystals were transformed into the I222 space group, leading to an extension of the maximum resolution to 1.42 Å. The dehydration of the crystals revealed a significant change in the five-water-molecules' binding mode in the vicinity of the catalytic diad, indicating that these molecules are quasi-stable. The pH profile analysis of log(kcat) gave two pKa values: pKa1 at 6.07 ± 0.07 and pKa2 at 7.98 ± 0.13. The site-directed mutagenesis of K13, T73 and N276 involved in the formation of the active-site water network revealed that the activities of these mutant variants were significantly reduced. These structural and kinetic data suggest that the five quasi-stable water molecules play an essential role in the catalysis of the cofactor-independent urate oxidation by reducing the energy penalty for the substrate-binding or an on-off switching for the proton-relay rectification.

Crystal structure of the catalytic unit of thermostable GH87 α-1,3-glucanase from Streptomyces thermodiastaticus strain HF3-3.

α-1,3-Glucan is a homopolymer composed of D-glucose (Glc) and it is an extracellular polysaccharide found in dental plaque due to Streptococcus species. α-1,3-Glucanase from Streptomyces thermodiastaticus strain HF3-3 (Agl-ST) has been identified as a thermostable α-1,3-glucanase, which is classified into glycoside hydrolase family 87 (GH87) and specifically hydrolyzes α-1,3-glucan with an endo-action. The enzyme has a potential to inhibit the production of dental plaque and to be used for biotechnological applications. Here we show the structure of the catalytic unit of Agl-ST determined at 1.16 Å resolution using X-ray crystallography. The catalytic unit is composed of two modules, a ß-sandwich fold module, and a right-handed ß-helix fold module, which resembles other structural characterized GH87 enzymes from Bacillus circulans str. KA-304 and Paenibacillus glycanilyticus str. FH11, with moderate sequence identities between each other (approximately 27% between the catalytic units). However, Agl-ST is smaller in size and more thermally stable than the others. A disulfide bond that anchors the C-terminal coil of the ß-helix fold, which is expected to contribute to thermal stability only exists in the catalytic unit of Agl-ST.

Immunochromatographic detection of human hemoglobin from deteriorated bloodstains due to methamphetamine contamination, aging, and heating.

Japanese police conduct highly sensitive and quick blood tests to detect human hemoglobin (Hb), because bloodstains left at a crime scene have probative value of circumstantial evidence in a criminal investigation. Although DNA detection from a bloodstain is a useful tool to identify an individual, doing so requires evidence that the bloodstain is of human origin. Stimulant drug abuse and dependence causes major social problems and crimes in Japan, and bloodstains are often found inside syringes seized from drug abusers. In this case, Hb often cannot be detected by conventional testing as high concentrations of stimulants, such as methamphetamine hydrochloride (MA), in blood trigger polymerization of Hb molecules, which become insoluble under non-reducing conditions and can no longer be detected by immunochromatographic detection kits. To overcome this problem, we analyzed methods to detect denatured Hb from bloodstains contaminated with MA. Reduction of polymerized Hb with a strong denaturing agent was required to solubilize polymers into monomers, suggesting that Hb aggregation is caused by aberrant formation of disulfide bonds. Based on these results, we established a pretreatment method, called Fukui's Reduction and Eiken's Dilution (FRED), that enables highly sensitive detection of human Hb from bloodstains mixed with MA by reducing and refolding of denatured Hb. This powerful method can be applied to blood that has been boiled or has otherwise deteriorated for over 20 years.

Structural insights into substrate recognition and catalysis by glycoside hydrolase family 87 α-1,3-glucanase from Paenibacillus glycanilyticus FH11.

The α-1,3-glucanase from Paenibacillus glycanilyticus FH11 (Agl-FH1), a member of the glycoside hydrolase family 87 (GH87), hydrolyzes α-1,3-glucan with an endo-action. GH87 enzymes are known to degrade dental plaque produced by oral pathogenic Streptococcus species. In this study, the kinetic analyses revealed that this enzyme hydrolyzed α-1,3-tetraglucan into glucose and α-1,3-triglucan with ß-configuration at the reducing end by an inverting mechanism. The crystal structures of the catalytic domain (CatAgl-FH1) complexed with or without oligosaccharides at 1.4-2.5 or 1.6 Å resolutions, respectively, are also presented. The initial crystal structure of CatAgl-FH1 was determined by native single-wavelength anomalous diffraction. The catalytic domain was composed of two modules, a ß-sandwich fold module, and a right-handed ß-helix fold module. The structure of the ß-sandwich was similar to those of the carbohydrate-binding module family 35 members. The glycerol or nigerose enzyme complex structures demonstrated that this ß-sandwich fold module is a novel carbohydrate-binding module with the capabilities to bind saccharides and to promote the degradation of polysaccharides. The structures of the inactive mutant in complexes with oligosaccharide showed that at least eight subsites for glucose binding were located in the active cleft of the ß-helix fold and the architecture of the active cleft was suitable for the recognition and hydrolysis of α-1,3-glucan by the inverting mechanism. The structural similarity to GH28 and GH49 enzymes and the results of site-directed mutagenesis indicated that three Asp residues, Asp1045, Asp1068, and Asp1069, are the most likely candidates for the catalytic residues of Agl-FH1. DATABASE: Structural data are available in RCSB Protein Data Bank under the accession numbers 6K0M (CatAgl-FH1), 6K0N (WT/nigerose), 6K0P (D1045A/nigerose), 6K0Q (D1068A/nigerose), 6K0S (D1069A/ nigerose), 6K0U (D1068A/oligo), and 6K0V (D1069A/oligo). ENZYMES: Agl-FH1, α-1,3-glucanase (EC3.2.1.59) from Paenibacillus glycanilyticus FH11.

Structural and biochemical characterisation of a novel alginate lyase from Paenibacillus sp. str. FPU-7.

A novel alginate lyase, PsAly, with a molecular mass of 33 kDa and whose amino acid sequence shares no significant similarity to other known proteins, was biochemically and structurally characterised from Paenibacillus sp. str. FPU-7. The maximum PsAly activity was obtained at 65 °C, with an optimum pH of pH 7-7.5. The activity was enhanced by divalent cations, such as Mg2+, Mn2+, or Co2+, and inhibited by a metal chelator, ethylenediaminetetraacetic acid. The reaction products indicated that PsAly is an endolytic enzyme with a preference for polymannuronate. Herein, we report a detailed crystal structure of PsAly at a resolution of 0.89 Å, which possesses a ß-helix fold that creates a long cleft. The catalytic site was different from that of other polysaccharide lyases. Site-directed mutational analysis of conserved residues predicted Tyr184 and Lys221 as catalytic residues, abstracting from the C5 proton and providing a proton to the glycoside bond, respectively. One cation was found to bind to the bottom of the cleft and neutralise the carboxy group of the substrate, decreasing the pKa of the C5 proton to promote catalysis. Our study provides an insight into the structural basis for the catalysis of alginate lyases and ß-helix polysaccharide lyases.

Crystal structure of the catalytic unit of GH 87-type α-1,3-glucanase Agl-KA from Bacillus circulans.

Glycoside hydrolase (GH) 87-type α-1,3-glucanase hydrolyses the α-1,3-glucoside linkages of α-1,3-glucan, which is found in fungal cell walls and extracellular polysaccharides produced by oral Streptococci. In this study, we report on the molecular structure of the catalytic unit of GH 87-type α-1,3-glucanase, Agl-KA, from Bacillus circulans, as determined by x-ray crystallography at a resolution of 1.82 Å. The catalytic unit constitutes a complex structure of two tandemly connected domains-the N-terminal galactose-binding-like domain and the C-terminal right-handed ß-helix domain. While the ß-helix domain is widely found among polysaccharide-processing enzymes, complex formation with the galactose-binding-like domain was observed for the first time. Biochemical assays showed that Asp1067, Asp1090 and Asp1091 are important for catalysis, and these residues are indeed located at the putative substrate-binding cleft, which forms a closed end and explains the product specificity.

Structural and functional characterization of a glycoside hydrolase family 3 ß-N-acetylglucosaminidase from Paenibacillus sp. str. FPU-7.

Chitin, a ß-1,4-linked homopolysaccharide of N-acetyl-d-glucosamine (GlcNAc), is one of the most abundant biopolymers on Earth. Paenibacillus sp. str. FPU-7 produces several different chitinases and converts chitin into N,N'-diacetylchitobiose ((GlcNAc)2) in the culture medium. However, the mechanism by which the Paenibacillus species imports (GlcNAc)2 into the cytoplasm and divides it into the monomer GlcNAc remains unclear. The gene encoding Paenibacillus ß-N-acetyl-d-glucosaminidase (PsNagA) was identified in the Paenibacillus sp. str. FPU-7 genome using an expression cloning system. The deduced amino acid sequence of PsNagA suggests that the enzyme is a part of the glycoside hydrolase family 3 (GH3). Recombinant PsNagA was successfully overexpressed in Escherichia coli and purified to homogeneity. As assessed by gel permeation chromatography, the enzyme exists as a 57-kDa monomer. PsNagA specifically hydrolyses chitin oligosaccharides, (GlcNAc)2-4, 4-nitrophenyl N-acetyl ß-d-glucosamine (pNP-GlcNAc) and pNP-(GlcNAc)2-6, but has no detectable activity against 4-nitrophenyl ß-d-glucose, 4-nitrophenyl ß-d-galactosamine and colloidal chitin. In this study, we present a 1.9 Å crystal structure of PsNagA bound to GlcNAc. The crystal structure reveals structural features related to substrate recognition and the catalytic mechanism of PsNagA. This is the first study on the structural and functional characterization of a GH3 ß-N-acetyl-d-glucosaminidase from Paenibacillus sp.

Crystal structure analysis and enzymatic characterization of γ-glutamyltranspeptidase from Pseudomonas nitroreducens.

Theanine (γ-glutamylethylamide) is an amino acid analog that reduces blood pressure and improves immune responses. The ϒ-glutamyltranspeptidase (GGT) from Pseudomonas nitroreducens IFO12694 (PnGGT) has a unique preference for primary amines as ϒ-glutamyl acceptors over standard L-amino acids and peptides. This characteristic is useful for the synthesis of theanine. We used X-ray crystallographic analysis to understand the structural basis of PnGGT's hydrolysis and transpeptidation reactions and to characterize its previously unidentified acceptor site. Structural studies of PnGGT have shown that key interactions between three residues (Trp385, Phe417, and Trp525) distinguish PnGGT from other GGTs. We studied the roles of these residues in the distinct biochemical properties of PnGGT using site-directed mutagenesis. All mutants showed a significant decrease in hydrolysis activity and an increase in transpeptidase activity, suggesting that the aromatic side chains of Trp385, Phe417, and Trp525 were involved in the recognition of acceptor substrates. Abbreviations: ϒ-glutamyl peptide, theanine, X-ray crystallography.

X-ray crystallographic analysis of the catalytic domain of α-1,3-glucanase FH1 from Paenibacillus glycanilyticus overexpressed in Brevibacillus choshinensis.

α-1,3-Glucanase hydrolyzes α-1,3-glucan, an insoluble linear α-1,3-linked homopolymer of glucose that is found in the extracellular polysaccharides produced by oral streptococci in dental plaque and in fungal cell walls. This enzyme could be of application in dental care and the development of fungal cell-wall lytic enzymes, but its three-dimensional structure has not been available to date. In this study, the recombinant catalytic domain of α-1,3-glucanase FH1 from Paenibacillus glycanilyticus FH11, which is classified into glycoside hydrolase family 87, was prepared using a Brevibacillus choshinensis expression system and purified in a soluble form. Crystals of the purified protein were produced by the sitting-drop vapor-diffusion method. Diffraction data were collected to a resolution of 1.6 Šusing synchrotron radiation. The crystals obtained belonged to the tetragonal space group P41212 or P43212, with unit-cell parameters a = b = 132.6, c = 76.1 Å. The space group and unit-cell parameters suggest that there is one molecule in the asymmetric unit.

Crystal Structure of Chitinase ChiW from Paenibacillus sp. str. FPU-7 Reveals a Novel Type of Bacterial Cell-Surface-Expressed Multi-Modular Enzyme Machinery.

The Gram-positive bacterium Paenibacillus sp. str. FPU-7 effectively hydrolyzes chitin by using a number of chitinases. A unique chitinase with two catalytic domains, ChiW, is expressed on the cell surface of this bacterium and has high activity towards various chitins, even crystalline chitin. Here, the crystal structure of ChiW at 2.1 Å resolution is presented and describes how the enzyme degrades chitin on the bacterial cell surface. The crystal structure revealed a unique multi-modular architecture composed of six domains to function efficiently on the cell surface: a right-handed ß-helix domain (carbohydrate-binding module family 54, CBM-54), a Gly-Ser-rich loop, 1st immunoglobulin-like (Ig-like) fold domain, 1st ß/α-barrel catalytic domain (glycoside hydrolase family 18, GH-18), 2nd Ig-like fold domain and 2nd ß/α-barrel catalytic domain (GH-18). The structure of the CBM-54, flexibly linked to the catalytic region of ChiW, is described here for the first time. It is similar to those of carbohydrate lyases but displayed no detectable carbohydrate degradation activities. The CBM-54 of ChiW bound to cell wall polysaccharides, such as chin, chitosan, ß-1,3-glucan, xylan and cellulose. The structural and biochemical data obtained here also indicated that the enzyme has deep and short active site clefts with endo-acting character. The affinity of CBM-54 towards cell wall polysaccharides and the degradation pattern of the catalytic domains may help to efficiently decompose the cell wall chitin through the contact surface. Furthermore, we clarify that other Gram-positive bacteria possess similar cell-surface-expressed multi-modular enzymes for cell wall polysaccharide degradation.

Hyperstabilization of Tetrameric Bacillus sp. TB-90 Urate Oxidase by Introducing Disulfide Bonds through Structural Plasticity.

Bacillus sp. TB-90 urate oxidase (BTUO) is one of the most thermostable homotetrameric enzymes. We previously reported [Hibi, T., et al. (2014) Biochemistry 53, 3879-3888] that specific binding of a sulfate anion induced thermostabilization of the enzyme, because the bound sulfate formed a salt bridge with two Arg298 residues, which stabilized the packing between two ß-barrel dimers. To extensively characterize the sulfate-binding site, Arg298 was substituted with cysteine by site-directed mutagenesis. This substitution markedly increased the protein melting temperature by ∼ 20 °C compared with that of the wild-type enzyme, which was canceled by reduction with dithiothreitol. Calorimetric analysis of the thermal denaturation suggested that the hyperstabilization resulted from suppression of the dissociation of the tetramer into the two homodimers. The crystal structure of R298C at 2.05 Å resolution revealed distinct disulfide bond formation between the symmetrically related subunits via Cys298, although the Cß distance between Arg298 residues of the wild-type enzyme (5.4 Å apart) was too large to predict stable formation of an engineered disulfide cross-link. Disulfide bonding was associated with local disordering of interface loop II (residues 277-300), which suggested that the structural plasticity of the loop allowed hyperstabilization by disulfide formation. Another conformational change in the C-terminal region led to intersubunit hydrogen bonding between Arg7 and Asp312, which probably promoted mutant thermostability. Knowledge of the disulfide linkage of flexible loops at the subunit interface will help in the development of new strategies for enhancing the thermostabilization of multimeric proteins.

Microplate Assay of α-Glucosidase and Its Inhibitors Based on the Direct Reduction of Molybdosilicate by Glucose.

A colorimetric method for monosaccharide determination (Anal. Sci., 2013, 29, 1021) was optimized for the high-throughput screening of α-glucosidase, which hydrolyzes an α-1,4-glycosidic bond of starch and related oligo- and polysaccharides, followed by the release of D-glucose from the non-reducing ends. In a microplate, 40 µL of a sample solution was mixed with 160 µL of a 50 mM Na2SiO3, 600 mM Na2MoO4, 1.5 M CH3COOH, and 20% (v/v) dimethyl sulfoxide solution, which was yellowish due to the formation of a yellow molybdosilicate. The mixture was kept at 80°C for 60 min. In the mixture, glucose reduced the Mo(VI) species directly to form a blue heteropolymolybdate(V/VI). Thus, 0.1 mM level glucose can be determined by the color change from yellow to blue. Since maltose cannot render the mixture blue as strongly as glucose, the present method has been successfully applied to a microtiter plate assay of α-glucosidase with the disaccharide. Also, the method has been applied to an assay of α-glucosidase inhibitors, acarbose and quercetin.

Nanoparticle-assisted laser desorption/ionization using sinapic acid-modified iron oxide nanoparticles for mass spectrometry analysis.

Iron oxide-based nanoparticles (NP) were covalently modified with sinapic acid (SA) through a condensation reaction to assist the ionization of both large and small molecules. The morphology of SA-modified NPs (SA-NP) was characterized by transmission electron microscopy (TEM), and the modification of the NP surface with SA was confirmed using ultraviolet (UV) and infrared (IR) spectroscopy. The number of SA molecules was estimated to be 6 per NP. SA-NP-assisted laser desorption/ionization was carried out on small molecules, such as pesticides and plant hormones, and large molecules, such as peptides and proteins. A peptide fragment from degraded proteins was detected more efficiently compared with conventional methods.

Colorimetric determination of fructose for the high-throughput microtiter plate assay of glucose isomerase.

A colorimetric method for the reducing monosaccharide determination is optimized for the assay of glucose isomerase, which converts glucose (Glc) to fructose (Fru). Test solution was mixed with 20-fold volume of the 50 mM Na2SiO3, 600 mM Na2MoO4, and 0.95 M HCl aqueous solution (pH 4.5), in which a yellow molybdosilicate species was formed. The mixture was kept at 70 °C for 30 min. Test solution containing 10 mM level Fru gave a remarkable blue reaction mixture, in which the Mo(VI) species was reduced by Fru to form a blue molybdosilicate species. The blueness increased with the Fru concentration. Glc cannot render the reaction mixture blue as strong as Fru. Thus, the colorimetric method can be used advantageously for the determination of 10 mM level Fru in the Glc isomerase reaction mixture, even in the presence of 100 mM level Glc, and has been applied successfully to the microtiter plate assay of the enzyme.

Overexpression, purification, and characterization of Paenibacillus cell surface-expressed chitinase ChiW with two catalytic domains.

Paenibacillus sp. strain FPU-7 produces several different chitinases and effectively hydrolyzes robust chitin. Among the P. FPU-7 chitinases, ChiW, a novel monomeric chitinase with a molecular mass of 150 kDa, is expressed as a cell surface molecule. Here, we report that active ChiW lacking the anchoring domains in the N-terminus was successfully overproduced in Escherichia coli and purified to homogeneity. The two catalytic domains at the C-terminal region were classified as typical glycoside hydrolase family 18 chitinases, whereas the N-terminal region showed no sequence similarity to other known proteins. The vacuum-ultraviolet circular dichroism spectrum of the enzyme strongly suggested the presence of a ß-stranded-rich structure in the N-terminus. Its biochemical properties were also characterized. Various insoluble chitins were hydrolyzed to N,N'-diacetyl-D-chitobiose as the final product. Based on amino acid sequence similarities and site-directed mutagenesis, Glu691 and Glu1177 in the two GH-18 domains were identified as catalytic residues.